In the installation of single ply waterproofing membranes it is common practice to interpose an underlayment membrane between the substrate and the waterproofing membrane. This is done in order to relieve the waterproofing membrane to some extent from the direct application of strains caused by shrinkage and expansion of the substrate due to environmental and other conditions. To a certain degree, such practice also tends to smooth out surface irregularities.
According to conventional practice, the underlayment membrane is applied to the substrate with a suitable adhesive, typically roofing cement or asphalt, or with mechanical fasteners, which must be applied in a separate time consuming and labor intensive operation, since sufficient care must be taken in the application steps in order to assure that the final waterproofing membrane complies with ASTM standards for resistance to uplifting pressure forces caused most often by winds blowing over the surface of the material. Additionally, the use of adhesives has the further disadvantage of limiting the repair or installation of waterproofing membranes to periods of warmer weather which are required for the use of adhesives.
It is not uncommon for the underlayment membrane to be formed from a reinforcing mat or web base layer impregnated with a bitumen/polymer mixture the same as or similar to the mixture which comprises the primary waterproofing constituent of the waterproofing membrane itself. However, improved methods of adhering single ply waterproofing membranes to a substrate which are less labor intensive and which provide increased strength and flexibility are desired.